What is BAC?
Blood alcohol content (BAC), also called blood alcohol concentration or blood alcohol level, is the amount of alcohol in your blood. In the US it is written as a percentage: a BAC of 0.08% means 0.08 grams of alcohol in every 100 milliliters of blood.
How this BAC calculator works
The calculator uses a Widmark-style estimate. It adds up the pure alcohol in everything you drank, spreads it over your body weight, and then subtracts what your body has cleared since the first drink.
Alcohol (fl oz) = drinks × size (fl oz) × ABV
Starting BAC % = alcohol × 5.24 ÷ (weight in lb × r)
BAC now % = starting BAC − 0.015 × hours since first drink
The ratio r reflects how much of the body takes up alcohol: 0.73 for men and 0.66 for women. Weight in kilograms or grams is converted to pounds (1 kg = 2.2046 lb), and sizes of other drinks are converted to US fluid ounces (1 fl oz = 29.57 ml, with a liter counted as 34 fl oz). The estimate never goes below 0%.
The calculator treats all the alcohol as if it were absorbed at the moment of the first drink and assumes your body clears 0.015% per hour from then on. The time until 0% is your current BAC divided by 0.015.
Drink sizes
In the US, a standard drink has about 0.6 fluid ounces (14 grams) of pure alcohol. That is roughly a 12 oz beer at 5% ABV, a 5 oz glass of wine at 12% ABV, or a 1.5 oz shot of 40% ABV liquor. Many real drinks are larger or stronger: a 16 oz pint of 7% craft beer is almost two standard drinks. If your drink is not listed, use the other drink row and enter its size and ABV from the label.
Typical effects by BAC level
| BAC | Typical effects |
|---|---|
| 0.001–0.029% | Looks and acts normal; subtle effects only |
| 0.030–0.059% | Mild euphoria, relaxation, lowered inhibitions, weaker concentration |
| 0.060–0.099% | Dulled feelings, impaired reasoning, depth perception, and side vision |
| 0.100–0.199% | Loud or exaggerated behavior, nausea, slow reflexes, staggering, slurred speech |
| 0.200–0.299% | Vomiting, confusion, severe loss of coordination, possible blackout |
| 0.300–0.399% | Stupor, lapses in consciousness, affected breathing and heart rate |
| 0.400–0.500% | Coma, possible death |
| Over 0.500% | High possibility of death |
Effects vary from person to person. Tolerance can hide how impaired you feel without lowering your BAC.
Frequently asked questions
What is the legal BAC limit for driving?
For drivers 21 and older, the limit is 0.08% in every US state except Utah, where it is 0.05%. Limits are lower for commercial drivers (0.04%) and for drivers under 21. You can be impaired, and charged, below these limits.
How long does it take to sober up?
BAC drops by about 0.015% per hour in this estimate. From 0.08% that is a little over five hours to reach 0%. Coffee, food, water, cold showers, and exercise do not speed it up; only time lowers BAC.
Why is BAC higher for women at the same weight?
On average, women have less body water per pound than men, so the same amount of alcohol is spread through a smaller volume. The calculator reflects this with a lower ratio (0.66 instead of 0.73).
How accurate is a BAC calculator?
It is a rough estimate. Real BAC depends on how fast you drank, whether you ate, your body composition, medications, and how quickly your own body clears alcohol, which varies widely between people. Only a breath or blood test measures BAC.
Limitations
This calculator is for education only and is not medical or legal advice. Never use it to decide whether you can drive, work, or do anything that needs your full attention. If you have been drinking, do not drive. If someone is hard to wake, breathing slowly, or vomiting while passed out, call 911.
What's changed
- Added grams as a body weight unit and shows drink sizes in both oz and ml.
- Launched.
References
- National Institute on Alcohol Abuse and Alcoholism, What Is a Standard Drink?
pure alcohol in a drink is its size times its alcohol by volume; one US standard drink has 0.6 fl oz